Commercially available infant formulas are typically produced using non-human milk. However the nutritional composition of human milk differs in some respects to that of non-human milk (such as cow, sheep, buffalo or goat).
Non-human whole milk such as cow, goat or sheep milk, contains a higher proportion of saturated fatty acids than human milk and is deficient in linoleic acid and alpha-linolenic acid, polyunsaturated fatty acids that are essential for normal infant growth and development. Also, butyric acid which is found in milk fat may cause putrid vomit in infants.
Therefore standard infant formulas are typically produced using low-fat dairy products such as skim milk. Using a reduced-fat dairy product means undesirable components in milk fat are not included in the infant formula, but it also means that phospholipid and (glyco)sphingolipid levels are significantly lower than those in human milk.
Research over the last 5-10 years has shown that increasing phospholipid and (glyco)sphingolipid levels in infant formulations to levels found in human milk (particularly ganglioside GM3, ganglioside GD3, ceramides and sphingomyelin) may lead to:                enhanced gut maturation, thereby reducing the risk of infection;        prevention of infections by modifying gut intestinal flora and competitively binding antigens;        prevention of the development of allergies; and        optimal neural development.        
It is therefore desirable to produce an infant formula containing sufficient levels of desirable lipids while minimising or eliminating undesirable ingredients.
One means currently used to achieve this is to add lipid-containing extracts and other individual ingredients to a base formulation thereby producing an infant formula with the desired nutritional profile. The lipid extracts may be produced using conventional extraction solvents (for example WO 94/18289 describes a method for extracting sphingomyelin from a phospholipid-containing fat concentrate using solvent extraction techniques). Such lipid extracts are expensive to produce. Furthermore, extensive toxicity and safety studies are required before regulatory approval in some jurisdictions can be obtained for their use.
Another means used to achieve this goal is to include buttermilk in infant formulas. Buttermilk is the aqueous by-product stream produced during one of three processes:                (1) Traditional butter manufacture using either the Fritz buttermaking or batch buttermaking process;        (2) Traditional production of butter-oil (also known as anhydrous milk fat or AMF) from cream as shown in FIG. 1;        (3) Production of butter-oil from cream using a two-sera process as shown in FIG. 2, where the buttermilk is produced by blending the secondary skim and beta-serum streams together.        
Infant formulas containing buttermilk contain lesser amounts of undesirable components of milk fat than non-human milk, but higher levels of phospholipids and (glyco)sphingolipids than reduced-fat dairy products. However, the levels of these desirable lipids are not high enough for buttermilk to be used in a whey-dominant infant formula in order to achieve phospholipid and (glyco)sphingolipid levels similar to those in human milk.
Supercritical extraction using carbon dioxide as the solvent is known to extract neutral lipids from buttermilk powders. Astaire J. C., Ward R., German J. B., and Jimenez-Flores R. (2003) Concentration of Polar MFGM Lipids from Buttermilk by Microfiltration and Supercritical Fluid Extraction J. Dairy Sci. 86, 2297-2307 describes the supercritical extraction of buttermilk using carbon dioxide as the solvent to produce a product rich in protein, and enhanced in levels of polar lipids. However, the buttermilk powder so produced still has low levels of polar lipids, at a maximum of 2% of the dry powder mass, and is thus unsuitable for infant formula.
One possible way to provide a suitable product would be to separate the protein components from the lipid components in a dairy product.
Dimethyl ether (DME) has previously been used in the extraction of lipids from raw egg yolk (Yano et al U.S. Pat. No. 4,157,404) and dried egg powder (Yano et al U.S. Pat. No. 4,234,619). The process causes the fractionation of the lipid and protein components into separate streams. In U.S. Pat. No. 4,157,404, Yano states that while lipids can be extracted from raw egg yolks (75% moisture content), the proteins are denatured. In U.S. Pat. No. 4,234,619, Yano states that proteins are not denatured if the egg yolk is dry, but the phospholipids can only be partially extracted.
WO 2004/066744 describes the extraction of lipids from an aqueous dairy stream using near critical extraction where dimethyl ether is the solvent. WO 2004/066744 also discloses that neither supercritical CO2 or subcritical dimethyl ether can extract lipids in useful yields from whey protein concentrate (WPC) dairy powders. However, this document does not disclose the extraction of lipids from powders rich in milk fat globule membrane material.
Attempts to extract lipids from dairy powder streams with high lactose contents (where high is at least 30% by mass of the total powder) by extraction using liquefied dimethyl ether have been unsuccessful.
It is therefore an object of the present invention to provide improved or alternative dairy products that can be used in infant formulations, and/or to at least provide the public with a useful choice.